Receptor tyrosine kinases (RTKs) are the main mediators of the signaling network that transmit extracellular signals into the cell, and control cellular differentiation and proliferation. Recent and rapid advances in our understanding of cellular signaling by RTKs, in normal and malignant cells, have brought to light the potential of RTKs as selective anti-cancer targets. Their activity is normally tightly controlled and regulated. Over expression of RTK proteins or functional alterations caused by mutations in the corresponding genes or abnormal stimulation by autocrine growth factor loops contribute to constitutive RTK signaling, resulting in dysregulated cell growth and cancer. The mechanisms of uncontrolled RTK signaling that lead to cancer have provided the rationale for anti-RTK drug development. Herceptin, Gleevec, and Iressa are the first examples of drugs which have successfully translated basic research on oncogenes into cancer therapeutics (Bennasroune et al., Crit Rev Oncol Hematol. 2004, 50, 23-38).
EGFR, a transmembrane glycoprotein, consisting of an extracellular ligand binding domain, a transmembrane domain and an intracellular tyrosine kinase domain, is a RTK whose activation initiates signal transduction through critical cellular pathways, such as those mediated by Akt (also known as Protein kinase B) and extracellular-signal-regulated kinases (ERK), and thus plays an important role in controlling cell homeostasis. Among the cognate ligands for EGFR, transforming growth factor- (TGF) and heparin-binding epidermal growth factor-like (HB-EGF) growth factor have been most strongly implicated in oncogenesis. Cell biological, in vitro and in vivo transgenic, clinical correlative, and therapeutic evidence point to a role for EGFR and its downstream cell signaling pathways, such as phosphoinositide 3-kinase (PI3K)/Akt and Ras/mitogen-activated protein kinase (MAPK) in the generation and malignant progression in various cancers. EGFR is mutated, over expressed, or aberrantly activated in different types of human tumors including head and neck, lung, and colorectal cancer, contributing to the malignant phenotype of cancer cells. Up-regulated EGFR is correlated with both poor prognosis and increased metastatic potential in numerous epithelial malignancies. Validation of EGFR as a target for therapeutic intervention in cancer has come from the clinical approval and use of various EGFR antagonists (including small molecule kinase inhibitors and monoclonal antibodies) in lung and colorectal cancer patients. Non-Small Cell Lung Cancer (NSCLC) patients with mutated EGFR show higher response rates and longer survival time when treated with EGFR kinase inhibitors such as Gefitinib and Erlotinib. EGFR inhibitors are being investigated as monotherapy and in combination with other targeted therapies in a wide range of tumor types (Nat. Rev. Cancer. 2010, 10, 760-74).
Although EGFR Tyrosine Kinase Inhibitors (TKIs) show a dramatic tumor response especially in NSCLC patients harboring EGFR mutations (such as L858R and Exon 19 deletion) and provide progression free survival and overall survival advantage, most patients relapse and develop resistance over time. Investigations of the reasons for resistance have revealed several mechanisms for resistance which include: i) secondary mutation in EGFR such as T790M; ii) amplification of c-Met, and iii) activation of TGFb-IL6-Jak/Stat axis.
Gefitinib, and Erlotinib, the two approved EGFR kinase inhibitors are highly effective against EGFR kinase domain mutants such as L858R, and delE746-A750. This is due to the increased affinity of the mutant proteins for Gefitinib, and Erlotinib as well as decreased affinity for ATP relative to WT protein. The clinical efficacy of these two drugs is ultimately limited by the appearance of acquired resistance as described above. The most common mechanism of resistance is the mutation of the gatekeeper residue Threonine 790 to Methionine (T790M). Interestingly, unlike the T315I mutation in ABL or the T670I in KIT (the targets of Imatinib in CML and GIST) both of which significantly alter drug binding to the target, T790M only modestly alters Gefitinib/Erlotinib binding to EGFR. In addition, T790M mutation restores the affinity of EGFR for ATP back to the WT level, thus contributing to the resistance of the mutation to Gefitinib/Erlotinib. This restored ATP affinity closes the therapeutic window provided by the diminished ATP affinity of the oncogenic mutants which are more easily inhibited by Gefitinib/Erlotinib relative to the WT EGFR.
There are number of second generation EGFR TKIs in clinical development (J. Clin. Oncol. 2010, 28, 3965-72; Mol. Cancer Ther. 2008, 7, 1880-89; J. Clin. Oncol. 2010, 28, 1301-07; Clin. Cancer Res. 2007, 13 (Suppl. 15), 4953s-4596s; J. Med. Chem. 2003, 46, 49-63; Chemistry & Biology 2013, 20, 146-149) Most of these inhibitors are irreversible inhibitors and have been touted to overcome T790M mediated resistance based on preclinical studies. These inhibitors are shown to be more potent against T790M mutation compared to Gefitinib or Erlotinib. The covalent binding nature of these inhibitors allows them to achieve greater potency (via greater occupancy of the ATP binding pocket) compared to reversible inhibitors. However, these inhibitors do not discriminate between WT EGFR and T790M mutation, thus limiting their clinical utility due to narrow therapeutic window.
All first and second generation reversible and irreversible EGFR, TKIs are based on quinazoline core. Recently there were few reports on selective EGFR T790M mutant inhibitors based on different cores (WO 2009/051822, WO 2012/167415, US 2012/0094999, WO 2010/129053 based on anilinopyrimidine core that fits the gatekeeper mutation while binding irreversibly to C797.
WZ4002 from Gatekeeper Pharmaceuticals is based on anilinopyrimidine core that fits the gatekeeper mutation while binding irreversibly to C797. In contrast to second generation irreversible TKIs, this inhibitor has greater potency towards double mutant EGFR (drug sensitizing L858R and drug resistant T790M) than either WT EGFR or drug sensitizing mutant EGFR both in vitro and in vivo. Hence, the expectation is that T790M mutant receptor will be effectively inhibited at drug concentration that will not affect WT EGFR, thus giving a bigger therapeutic window. Thus, a number of EGFR T790M inhibitors are known and some are being developed for medical uses (J. Clin. Oncol. 2010, 28, 3965-72; Mol. Cancer Ther. 2008, 7, 1880-89; J. Clin. Oncol. 2010, 28, 1301-07; Clin. Cancer Res. 2007, 13 (Suppl. 15), 4953-4596). Different classes of compounds may have different degrees of potency and selectivity for inhibiting EGFR T790M. There is a need to develop alternative EGFR T790M inhibitors with improved potency and/or beneficial activity profiles and/or beneficial selectivity profiles and/or increased efficacy and/or improved safety profiles (such as reduced side effects) and/or improved pharmacokinetic properties.